Salt marsh restoration surprise: A subordinate species accumulates and shares nitrogen while outcompeting salt marsh dominants

Selectively planting native species could guide ecosystem development toward wetland restoration targets, once we understand how influential species function, alone and in combination. Knowing that Triglochin concinna (arrow grass, Juncaceae) accumulates N in its perennial roots, we asked how it would influence N dynamics on an excavated salt marsh plain at Tijuana Estuary, in southern California. We hypothesized that it would (a) accumulate N in roots and shoots, (b) reduce biomass of other marsh plain plants or, alternatively, (c) share N with neighbors as its litter decomposed and released N. We used 15N stable isotope enrichment to quantify N transfer between Triglochin and the marsh plain’s seven-species halophyte assemblage in field and greenhouse experiments. We also examined the effect of Triglochin on individual marsh plain species’ biomass and N accumulation. Triglochin had low shoot biomass (0.96 ± 0.5 g m−2 in field plots and 17.64 ± 2.2 g m−2 in greenhouse pots), high root:shoot ratios (4.3 in the field and 2.0 in the greenhouse), and high tissue N content (1.9 ± 0.2% in the field and 1.7 ± 0.1% in the greenhouse). Two productive perennials, Sarcocornia pacifica (pickleweed) and Frankenia salina (alkali heath), outgrew Triglochin; yet these biomass dominants produced 44%–45% less shoot biomass in greenhouse pots with Triglochin than without. However, we did not find this reduction in the field where roots were unconfined. In the greenhouse, δ15N values were higher for species grown with 15N-enriched Triglochin, indicating that this species made N available to its neighbors. The δ15N values for plants grown in the field exceeded background levels, also indicating that the marsh plain assemblage took up N released by Triglochin. We conclude that Triglochin can influence the restoration of salt marsh vegetation by accumulating N and releasing its tissue N to neighbors as leaves and roots decompose, while simultaneously reducing the biomass of neighbors. The seasonally deciduous Triglochin is low in shoot biomass, yet competitively superior in N uptake. Because this often-ignored species has limited tidal dispersal, we suggest restoration plantings, including tests of its ability to facilitate diversity where S. pacifica, the marsh plain dominant, might otherwise form monocultures

Evaluating the effects of Southern Resident orcas recovery actions and external threats in the marine ecosystem of Puget Sound

We apply two ecosystem models, the Atlantis Model for Puget Sound and the Salish Sea Atlantis Model, to simulate the recommendations of the Southern Resident Orca Task Force for recovery of the endangered Southern Resident Killer Whales (“Southern Residents”) in the Salish Sea. The downturn of the Southern Residents has been attributed to multiple, co-occurring anthropogenic and ecological pressures that are being addressed through the recommendations of the Orca Task Force. Atlantis is a spatially-explicit ecosystem modeling platform that simulates oceanography and biochemistry, food-web interactions, fisheries, and dependence of species on biogenic and physical habitat. We are evaluating the ecosystem-level impacts of recovery actions aimed at enhancing population growth and long-term sustainability of the Southern Residents and the future cumulative impacts from human population growth, oil spills, and climate change. We are addressing three objectives by simulating long-term dynamics using the two ecosystem models built in the Atlantis framework that span the full Salish Sea range of Southern Residents: (1) Analyze whether recovery actions for Southern Residents will support or hinder other conservation objectives; (2) Reveal potential tradeoffs inherent in the proposed recovery actions, both via direct effects and indirect (trophic) pathways; (3) Examine future cumulative threats from population growth, ocean warming, and oil spills. We are evaluating these scenarios in terms of abundance, size, diets, catch, and ecosystem indicators. We are generating information on ecosystem-level tradeoffs, the probability of success of recovery actions, and economic impacts, that can help managers and policy makers reconcile potentially conflicting unintended consequences that are likely to arise in response to bold conservation actions for Southern Resident recovery and from future cumulative threats

An Atlantis Ecosystem Model for the Gulf of Mexico supporting Integrated Ecosystem Assessment

The Gulf of Mexico supports a high biological diversity and biomass of fish, seabirds, and mammals; in this region, multiple commercial and recreational fishing fleets operate providing economic resources for local populations. The Gulf is also the site of important oil and gas production and tourism. As a result of intensive human use, the Gulf is subject to various impacts, including oil spills, habitat degradation, and anoxia. Management of this Large Marine Ecosystem requires an ecosystem-based management approach that provides a holistic approach to resource management. The Gulf of Mexico is managed as part of NOAA\u27s Integrated Ecosystem Assessment Program (IEA). This program considers the development of ecosystem models as a tool for ecosystem-based fisheries management (EBFM) and to support the different stages in the IEA process, particularly testing the effects of alternative management scenarios. As part of this program, we have parametrized an Atlantis ecosystem model for the Gulf of Mexico, including major functional groups, physiographic dynamics, and fishing fleets. The Gulf of Mexico (GOM) Atlantis model represents a collaboration between the University of South Florida, the University of Miami, the Southeast Fisheries Science Center, the National Coastal Data Development Center, and other contributors --Executive summary

An Atlantis Ecosystem Model for the Gulf of Mexico supporting Integrated Ecosystem Assessment

The Gulf of Mexico supports a high biological diversity and biomass of fish, seabirds, and mammals; in this region, multiple commercial and recreational fishing fleets operate providing economic resources for local populations. The Gulf is also the site of important oil and gas production and tourism. As a result of intensive human use, the Gulf is subject to various impacts, including oil spills, habitat degradation, and anoxia. Management of this Large Marine Ecosystem requires an ecosystem-based management approach that provides a holistic approach to resource management. The Gulf of Mexico is managed as part of NOAA\u27s Integrated Ecosystem Assessment Program (IEA). This program considers the development of ecosystem models as a tool for ecosystem-based fisheries management (EBFM) and to support the different stages in the IEA process, particularly testing the effects of alternative management scenarios. As part of this program, we have parametrized an Atlantis ecosystem model for the Gulf of Mexico, including major functional groups, physiographic dynamics, and fishing fleets. The Gulf of Mexico (GOM) Atlantis model represents a collaboration between the University of South Florida, the University of Miami, the Southeast Fisheries Science Center, the National Coastal Data Development Center, and other contributors --Executive summary

Ocean Futures Under Ocean Acidification, Marine Protection, and Changing Fishing Pressures Explored Using a Worldwide Suite of Ecosystem Models

Ecosystem-based management (EBM) of the ocean considers all impacts on and uses of marine and coastal systems. In recent years, there has been a heightened interest in EBM tools that allow testing of alternative management options and help identify tradeoffs among human uses. End-to-end ecosystem modeling frameworks that consider a wide range of management options are a means to provide integrated solutions to the complex ocean management problems encountered in EBM. Here, we leverage the global advances in ecosystem modeling to explore common opportunities and challenges for ecosystem-based management, including changes in ocean acidification, spatial management, and fishing pressure across eight Atlantis (atlantis.cmar.csiro.au) end-to-end ecosystem models. These models represent marine ecosystems from the tropics to the arctic, varying in size, ecology, and management regimes, using a three-dimensional, spatially-explicit structure parametrized for each system. Results suggest stronger impacts from ocean acidification and marine protected areas than from altering fishing pressure, both in terms of guild-level (i.e., aggregations of similar species or groups) biomass and in terms of indicators of ecological and fishery structure. Effects of ocean acidification were typically negative (reducing biomass), while marine protected areas led to both “winners” and “losers” at the level of particular species (or functional groups). Changing fishing pressure (doubling or halving) had smaller effects on the species guilds or ecosystem indicators than either ocean acidification or marine protected areas. Compensatory effects within guilds led to weaker average effects at the guild level than the species or group level. The impacts and tradeoffs implied by these future scenarios are highly relevant as ocean governance shifts focus from single-sector objectives (e.g., sustainable levels of individual fished stocks) to taking into account competing industrial sectors\u27 objectives (e.g., simultaneous spatial management of energy, shipping, and fishing) while at the same time grappling with compounded impacts of global climate change (e.g., ocean acidification and warming)

Ecosystem-Based Harvest Control Rules for Norwegian and US Ecosystems

Management strategy evaluation (MSE) provides a simulation framework to test the performance of living marine resource management. MSE has now been adopted broadly for use in single-species fishery management, often using a relatively simple “operating model” that projects population dynamics of one species forward in time. However, many challenges in ecosystem-based management involve tradeoffs between multiple species and interactions of multiple stressors. Here we use complex operating models, multi-species ecosystem models of the California Current and Nordic and Barents Seas, to test threshold harvest control rules that explicitly address the linkage between predators and prey, and between the forage needs of predators and fisheries. Specifically, within Atlantis ecosystem models we focus on how forage (zooplankton) availability affects the performance of harvest rules for target fish, and how these harvest rules for fish can account for environmentally-driven fluctuations in zooplankton. Our investigation led to three main results. First, consistent with studies based on single-species operating models, we found that compared to constant F = FMSY policies, threshold rules led to higher target stock biomass for Pacific hake (Merluccius productus) in the California Current and mackerel (Scomber scombrus) in the Nordic and Barents Seas. Performance in terms of catch of these species varied depending partly on the biomass and recovery trajectory for the simulated stock. Secondly, the multi-species operating models and the harvest control rules that linked fishing mortality rates to prey biomass (zooplankton) led to increased catch variability; this stemmed directly from the harvest rule that frequently adjusted Pacific hake or mackerel fishing rates in response to zooplankton, which are quite variable in these two ecosystems. Thirdly, tests suggested that threshold rules that increased fishing when productivity (zooplankton) declined had the potential for strong ecosystem effects on other species. These effects were most apparent in the Nordic and Barents Seas simulations. The tests of harvest control rules here do not include uncertainty in monitoring of fish and zooplankton, nor do they include uncertainty in stock assessment and implementation; these would be required for full MSE. Additionally, we intentionally chose target fish with strong mechanistic links to particular zooplankton groups, with the simplifying assumption that zooplankton biomass followed a forced time series. Further developing and testing of ecosystem-level considerations can be achieved with end-to-end ecosystem models, such as the Atlantis models applied here, which have the added benefit of tracking the follow-on effects of the harvest control rule on the broader ecosystem

Indirect Effects of Conservation Policies on the Coupled Human-Natural Ecosystem of the Upper Gulf of California

High bycatch of non-target species and species of conservation concern often drives the implementation of fisheries policies. However, species- or fishery-specific policies may lead to indirect consequences, positive or negative, for other species or fisheries. We use an Atlantis ecosystem model of the Northern Gulf of California to evaluate the effects of fisheries policies directed at reducing bycatch of vaquita (Phocoena sinus) on other species of conservation concern, priority target species, and metrics of ecosystem function and structure. Vaquita, a Critically Endangered porpoise endemic to the Upper Gulf of California, are frequently entangled by finfish gillnets and shrimp driftnets. We tested five fishery management scenarios, projected over 30 years (2008 to 2038), directed at vaquita conservation. The scenarios consider progressively larger spatial restrictions for finfish gillnets and shrimp driftnets. The most restrictive scenario resulted in the highest biomass of species of conservation concern; the scenario without any conservation measures in place resulted in the lowest. Vaquita experienced the largest population increase of any functional group; their biomass increased 2.7 times relative to initial (2008) levels under the most restrictive spatial closure scenario. Bycatch of sea lions, sea turtles, and totoaba decreased \u3e 80% in shrimp driftnets and at least 20% in finfish gillnet fleets under spatial management. We found indirect effects on species and ecosystem function and structure as a result of vaquita management actions. Biomass and catch of forage fish declined, which could affect lower-trophic level fisheries, while other species such as skates, rays, and sharks increased in both biomass and catch. When comparing across performance metrics, we found that scenarios that increased ecosystem function and structure resulted in lower economic performance indicators, underscoring the need for management actions that consider ecological and economic tradeoffs as part of the integrated management of the Upper Gulf of California

Full Compliance with Harvest Regulations Yields Ecological Benefits: Northern Gulf of California Case Study

1. The Northern Gulf of California is an ecologically important marine area with a high degree of biodiversity, endemism and productivity. Mounting conservation concerns have prompted researchers to propose new management regulations, restricting fishing and protecting sensitive species. Compliance with existing regulations is poor. Rules that are currently in place, if followed, may go a long way towards achieving the ecological goals of management. 2. We conduct a review of existing fisheries regulations in this area. Then, using a spatially explicit marine ecosystem model (Atlantis), we estimate the benefits of compliance with existing fisheries regulations. 3. Under a full compliance scenario, we find large increases in protected species biomass within 25 years and a slowed rate of ecosystem degradation because of fishing. However, full compliance costs the fishing industry about 30% of its annual revenue. 4. We parse out the benefits offered by management instruments (including spatial management protections, seasonal fishery closures, gear restrictions, cessation of illegal fishing and vessel buy-out programmes) and conclude that a suite of measures is needed to address major conservation objectives. 5. Synthesis and applications. This exercise quantifies the benefits of improved fisheries enforcement and provides a benchmark by which the value of future regulatory amendments can be assessed. Where compliance with existing regulations is poor, conservation goals may be better served by strengthening enforcement than by enacting new rules and legislation